This invention relates to electric components and more particularly to composite electrically conductive leads for such components.
In manufacturing certain electrical components, such as rectifiers, lead material is connected as by brazing to an electrically and thermally conductive base such as a block of molybdenum which, after having a semiconductor element mounted thereon, is sealed in glass by subjecting the assembly to a temperature sufficient to melt the glass. The assembly is then normally subjected to a coating operation such as a barrel plating operation, to apply a thin coating of tin or other suitable non-corrosive material to the surface of the lead material.
Various materials have been employed as the lead material including copper which, of course, has excellent electrical conductivity characteristics. However copper suffers from the disadvantage of being too easily bent, particularly in the annealed condition after having been subjected to the glass sealing operation so that subsequent barrel plating operations result in many of the leads being bent thereby rendering the devices useless or at least in need of corrective processing.
Another material which has been used for such electric leads is a copper alloy, zirconium copper. This material has acceptable electrical conductivity, in the order of 93% IACS (International Accepted Copper Standard) that is, the conductivity of zirconium copper is approximately 93% that of copper. However, this alloy is significantly more expensive than copper, in the order of four times as much and is subject to discoloration at elevated temperatures (e.g. above 1600.degree. F.).
Yet another material which has been used for such electric leads is a composite material, a steel core clad with copper. Due to the steel core this material is sufficiently strong even after the glass sealing operation and has the added benefit of being magnetically attractable so that magnetic handling equipment can be used to facilitate processing of the electronic components. For example, the components can be magnetically oriented in a given direction to facilitate automatic inspection techniques. The electrical conductivity can be adjusted somewhat by varying the ratio of the copper to steel in the composite however, in any event, it is somewhat lower than copper or zirconium copper, i.e., in the order of 80% or less compared to copper. In certain devices, such as high power rectifiers, it is desirable to have higher conductivity characteristics but at levels of 70% or higher the magnetic characteristic becomes too small to be useful. The most difficult problem that this material has presented however, is that it is very difficult to produce the composite so that the steel core is concentric relative to the copper layer and lack of concentricity results in lower yields due to thermostatic deformation or bending of the leads when subjected to elevated temperatures as when the leads are brazed to the molybdenum block which involves subjecting at least a portion of the lead to a temperature in the order of 180.degree. F.
It is therefore an object of the present invention to provide electric lead material for use with electronic devices capable of withstanding elevated processing temperatures. Another object is the provision of composite wire material which has high electrical conductivity and which has improved concentricity characteristics. Yet another object is the provision of a low cost electric lead material which is sufficiently strong, even after being subjected to elevated temperatures normally incident to the manufacture of associated components, to withstand further processing without being subject to bending of the leads.
Various other objects and advantages will appear from the following description of one embodiment of the invention and the novel features will be particularly pointed out hereinafter in connection with the appended claims.